Gypsum plaster



United States Patent Ofitice 3,942,537 Patented July 3, 1962 3,042,537 GYPSUM PLASTER W; J. Newell, 421 Conner Ave., and James E. Madden, 4709 Calmont St., both of Fort Worth, Tex. No Drawing. Filed June 23, 1961, Ser. No. 125,900 8 Claims. (Cl. 106 110) This invention relates to an improved gypsum plaster. More particularly it relates to gypsum plasters having a workability and a plasticity is a continuation-in-part of Newell et al. application Serial Number 844,637, filed October 6, 1959, and now abandoned.

One object of the invention is to produce a stronger gypsum plaster than those heretofore commercially available.

Still another ob ect is to provide a gypsum plaster having greatly enhanced cohesive properties which facilitate the even application of relatively thick coats on vertical surfaces without slippage.

Still a further object of the invention is to minimize or to eliminate the requirement of lime as an addition sisting predominantly of particles up to about 20 milli- Additions as litt e as between and 6.70 by Weight of the gypsum in the plaster composition greatly improve cohesiveness, workability, plasticity and set amount of lime, Amounts of the silica up to about 1% are generally completely adequate for the purpose. More can be added, e.g. up to about 2%, to produce an especially smooth plaster for special applications, but will generally not be The benefits of our Worthwhile. Amounts above introduce difficult mixing problems because of the very low bulk density of the silica.

We have found particularly suitable for our purpose silica produced by the vapor phase hydrolysis of SiCl at vapor in a hydrogen-oxygen flame.

The siliceous produce which it is preferred to use in the gypsum plasters of the present invention is a solid theory, we believe that silica produced in the manner described above and which has never been condensed from being noted that the addition of as little as Mr by Weight results in a noticeable improvement in the gypsum plasters of this invention as compared with those heretofore known.

Other finely divided silica solids may be used provided they have properties which are generally similar to and equivalent to those set forth above. For instance the silica could be obtained by the vapor phase hydrolysis at This invention will be more fully understood from a consideration of the following description in which a the invention.

Since e are numerous generally accepted classes of ther gypsum plasters, the present invention will be described With illustrative which lime has been found to be useful as a spreading In each of the gypsum plasters exemplified, the addition of between /2% and by Weight of finely divided silica of the type described above resulted in a marked improvement in workability.

cause the hme putty is high in shrinkage, it is very hard to keep the plaster from checking when using the ratio prior art above. There is a tendency in practice to add even more lime putty and sand than the relative proportions indicated above in an efiort to reduce the tendency to check and to reduce the tendency of the trowel to drag when applying the plaster. Plasters formulated with less lime putty, esg. those identified as A and B above exhibited a materially diminished tendency to form hair-or chip-cracks and worked more smoothly than the mixtures heretofore used.

WHITE COAT STANDARD MIX EXAMPLE The following tests were made to determine the effect of different amounts of Cab-o-sil in imparting plasticity, workability, and spreadability to Keenes cement. In each test, the stated amount of Cab-o-sil was mixed with 100 parts of Keenes cement and the mix worked up in conventional manner. Each mix was then tested to determine its workability.

(1) A part Cab-o-sil: This plaster mix had excellent plasticity, spreadability, and a good, pliable, fat feel under trowel.

(2) 2 parts C-ab-o-sil: Plasticity and smoothness was markedly increased as compared with (1).

(3) 3 parts Cab-o-sil: This plaster possessed somewhat greater plasticity and smoothness than (2).

(4) 4 parts Cab-o-Sil: This plaster showed a slight increase in plasticity and smoothness as compared with (3).

(5) 5 parts Cab-o'sil: This plaster was practically indistinguishable from (4).

The term gypsum as employed in this specification is intended to mean either partially or completely dehydrated calcium sulfate and includes therefore anhydrite (CaSO the hemihydrate, CaSO /2H O; plaster of Paris and similar calcium sulfates which may be further hydrated.

Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those s lled in the art that the principles of this invention can be embodied in other forms but within the scope of the claims.

We claim:

1. A gypsum plaster consisting essentially of gypsum and a minor amount of colloidal silica obtained by vapor phase hydrolysis of a hydrolyzable silicon compound at a temperature below the vaporization temperature of silica, said colloidal silica comprising about A to about 10% by weight of said gypsum.

2. A gypsum plaster consisting essentially of gypsum and a minor amount of colloidal silica obtained by vapor phase hydrolysis of a hydrolyzable silicon compound at a temperature below the vaporization temperature of silica, said colloidal silica comprising about A% to about 2% by weight of said gypsum.

3. The gypsum plaster of claim 2 in which the hydrolyzable silicon compound is SiCl 4. The gypsum plaster of claim 2 which contains, in addition, lime in an amount which is substantially less than that required for equivalent workability in the absence of said colloidal silica.

5. The gypsum plaster of claim 3 which contains, in addition, lime in an amount which is substantially less than that required for equivalent workability in the absence of said colloidal silica.

6. The gypsum plaster of addition, sand filler.

7. The gypsum plaster of claim 4 which contains, in addition, sand filler.

8. The gypsum plaster of claim 5 which contains, in addition, sand filler.

claim 3 which contains, in

Rock Products, January 1956, page 82. Ind. Eng. Chem, volume 51, pages 232-238, March 1959. 

1. A GYPSUM PLASTER CONSISTING ESSENTIALLY OF GYPSUM AND A MINOE AMOUNT OF COLLOIDAL SILICA OBTAINED BY VAPOR PHASE HYDROLYSIS OF A HYDROLYZABLE SILICON COMPOUND AT A TEMPERATURE BELOW THE VAPORIZATION TEMPERATURE OF SILICA, SAID COLLOIDAL SILICA COMPRISING ABOUT 1/4% TO ABOUT 10% BY WEIGHT OF SAID GYPSUM. 